Synthesis, ceramic conversion and microstructure evolution of HfC-based nanocomposites derived from precursors with different nitrogen contents

Precursors with different nitrogen contents were synthesised using hafnium (IV) chloride (HfCl4), dicyandiamide (DICY) and triethylamine (Et3N) as raw materials and were used for preparing Hf-based nanocomposites. The synthesis, ceramic conversion and microstructural evolution of HfC-based nanocomposites derived from precursors with different nitrogen contents were investigated. The results indicate that the composition of the synthesised precursors can be controlled by adjusting the molar ratio of HfCl4 and dicyandiamide. Pyrolysis of the precursors at 1200 degrees C led to the formation of Hf2CN- or HfN-based ceramics. As the nitrogen content of the synthesised precursors increased, the Hf2CN crystallites present in the ceramics annealed at 1200 degrees C gradually transformed to HfN. Furthermore, at 1600 degrees C, the HfN and Hf2CN phases gradually converted to HfC(N). The results also indicate that nitrogen favours the sintering of the obtained nanocomposites. The HfC-based ceramics should be promising for application as high-performance composite ceramics. (C) 2018 Elsevier B.V. All rights reserved.